removeUnlessInstanceOf

Removes any items in the list that are not type A and returns a MutableCollection<A> with the remaining items.

The mutable equivalent to Collection.filterIsInstance.

Note: this function removes in-place only if A is a MutableList, otherwise it clears the collection and re-adds the values.

Removes any items in the list that are not type A and returns a MutableList<A> with the remaining items.

The mutable equivalent to List.filterIsInstance.

sealed interface Item {
    data class SoldOut(val name: String) : Item
    data class Available(val name: String, val remaining: Int) : Item
}

data class Catalog(val items: List<Item>)

fun filterAvailable(catalog: Catalog) =
    catalog.copy {
        items.removeUnlessInstanceOf<Item.Available>()
    }

The returned value is a typed mutable collection where we can do further modifications with the right type, saving you having to do further type checks.

items.removeUnlessInstanceOf<Item.Available>()
     .mutateAll { item -> item.remaining-- }

Removes any items in the list that are not type A and returns a MutableSet<A> with the remaining items.

The mutable equivalent to Set.filterIsInstance.